The present invention relates generally to a portable data carrier designed for use in a contactless mode, and in particular to a method and apparatus for regulating power delivered to such a portable data carrier.
Portable data carriers (e.g., smart cards or chip cards are known to include a plastic substrate in which a semiconductor device (i.e., integrated circuitxe2x80x94IC) is disposed for retaining digital data. This digital data may constitute program instructions, user information, or any combination thereof. Moreover, these smart cards are known to be operational in a contacted mode, whereby an array of contact points disposed on the plastic substrate and interconnected with the semiconductor device is used to exchange electrical signals between the chip card an external card reader, or terminal. Similarly, there exists smart cards that operate in a contactless mode, whereby a radio frequency (RF) receiving circuit is employed to exchange data between the card and a card terminal. That is, the card need not come into physical contact with the card terminal in order to exchange data therewith, but rather must simply be placed within a predetermined range of the terminal.
Additionally, there exist smart cards that are alternatively operational in either a contacted mode or a contactless mode. Such cards are equipped with both RF receiving circuitry (for contactless operations) as well as an array of contact pads (for contacted operations). These smart cards are commonly referred to as combination cards, or combi-cards. It should be noted that in both the contact-only card and the combi-card arrangements, the array of contact pads typically conform to the ISO Standard 7816, which standard is incorporated herein by reference.
One of the problems of today""s contactless smart card applications is the limited amount of information that can be modulated onto the carrier frequency. Indeed, some applications prohibit any modulation of the carrier frequency, thereby requiring another means for extracting transmitted information signals, other than the power signal transmitted on the carrier frequency, fc. Of course, there is a need for a transport of data signals as well as a clock signal that is to be used by the processing element of the smart card.
Prior art applications have tried to solve this problems using two-frequency systems, whereby the power signal was transmitted on a first frequency, and information (e.g. data signals and timing information) were transmitted on a second frequency. This implementation, which required additional circuitry on board the smart card where space is limited, resulted in a complex and costly solution. That is, because the discrete components required to receive RF signals from a terminal/reader, account for a great deal of the cost and complexity of a smart card system, adding another discrete receiving circuit to the card substantially increases the cost.
Accordingly, there exists a need for a method and apparatus for recovering a clock signal that is not constrained by the shortcomings of the prior art. In particular, a smart card apparatus that was able to reliably receive information without using the carrier frequency, and without adding substantial cost to the manufacture of the card, would be an improvement of the prior art.